The present invention relates to a stone or ballast metering system for a railroad track maintenance vehicle.
The tremendous forces exerted on railroad track as trains and other rail vehicles move over the track results in displacement of the rails and ties within the stones or "ballast." In particular, the vertical position of the ties within the track ballast changes, usually with the ties settling deeper into the ballast, changing the height of the track. Accordingly, periodic realignment of the railroad track within the bed is necessary to restore the track to its desired configuration. Realignment is performed by either a tamper or a stone blower.
A tamper includes a jacking mechanism which grasps and lifts the rails and ties attached thereto. The tamper also includes blades which penetrate the ballast and are vibrated to force the ballast back under the lifted ties to return the track to a desired vertical position.
A stone blower also includes a jacking mechanism which grasps and lifts the rails and ties. However, rather than blades, the stoneblower includes tubes which penetrate the ballast and force new or additional stones beneath the ties. More particularly, a stoneblower is a vehicle that travels upon the track rails and carries a track lifting device, a number of workheads, a source of compressed air, a supply of ballast stones, and a stone metering system. The workheads each include one or more blow tubes through which ballast stone is blown by compressed air. In operation, the track lifting device raises the track rails and the ties to which the rails are secured, which creates a void beneath the ties. The blow tubes are forced into the track bed adjacent the raised ties to direct a measured quantity of ballast stone under the ties. The amount of stone is determined by the desired amount of lift.
The amount of ballast stone blown beneath each tie is crucial to the proper level of the tracks. The ballast stone must be delivered to the workheads in the proper quantity. It is the function of the stone metering system to ensure that the proper quantity of stone is delivered from the supply of ballast stones to the workheads.
In the past, vibratory chute style stone metering systems have been employed. This type of system utilizes a feeder pan to receive the desired amount of stone by weight. The measured stone is passed in bulk to a vibratory chute type feeder. The vibratory chute feeds the measured stone to the blow tubes at a fairly constant rate. This type of stone metering system is difficult to incorporate into the configuration and profile of the stoneblower. In addition, the precision of this design is adversely affected by a variety of elements, such as track cant, stone moisture content, track grade, and cycle time.
Another known type of stone metering system includes a number of auger conveyors which convey and meter stone to the workheads. Each auger conveyor includes an auger screw housed within a casing. As the auger screw is rotated, stone is conveyed along the flights of the screw. The amount of stone supplied to the blow tubes is measured by calculating the flow rate of the auger conveyor and monitoring the revolutions of the auger screw. Auger systems include an auger conveyor for each blow tube. Auger type stone metering systems have a variety of shortcomings. First, degradation (i.e. pulverization) of the stone during the conveying process produces "fines" (i.e. powdered stone) which reduces the accuracy of the metering system. Second, pulsed output of stone from the metering auger can lead to uneven distribution of stone. Third, the required multiplicity of augers is relatively expensive, bulky, and difficult to incorporate into the profile of a stoneblower.